Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
Crop losses due to infection by plant pathogens (phytopathogens) such as fungal and insect pathogens are a major problem in the agricultural industry and each year, millions of dollars are spent on the application of fungicides to curb these losses (Oerke and Dehne (2004) Crop Protection 23:275-285). There is a need to identify new anti-phytopathogen strategies. This is particularly important given the propensity for pathogens to develop resistance. Fungal infection of human and non-human subjects can also lead to significant discomfort and major health issues. Pathogenic fungi are also a serious concern for human health and for the economy. Human fungal pathogens cause life-threatening hospital-acquired diseases with high mortality rates as well as less severe superficial infections.
Plants have evolved to produce peptides to protect against pathogens. Their specificity is likely influenced by the evolutionary in response to exposure to various pathogens.
Plant defensins represent one type of anti-pathogen molecule. There is a wide variety of defensins with differing spatial and temporal patterns of expression and spectra of activity. Generally, plant defensins are divided into two major classes. Class I defensins consist of an endoplasmic reticulum (ER) sequence followed by a mature defensin domain. Class II defensins are produced as larger precursors with C-terminal pro-domains or pro-peptides (CTPPs) of about 33 amino acids in addition to the ER signal sequence and mature domain.
The mechanism underlying the specificity of these peptides is yet to be fully elucidated, although interactions with plasma membrane components are presumed to be involved. Since membrane permeabilization is a common activity of many anti-pathogen peptides and the membrane composition of various cell types is highly variable, the presence of specific lipids is postulated in some cases to be responsible for the efficacy of anti-pathogen peptides.
Plant pathogens induce significant plant yield loss and current strategies for pathogen control are both expensive and potentially damaging to the environment. Given the need to improve the economy of agriculture production, new strategies are required for protecting agronomic and ornamentally important plants from a range of diseases, especially fungal disease. Pathogenic fungi are also a serious concern for human health and for the economy. Current therapies require long treatment regimes and patients often suffer from associated liver toxicity. Resistance to current therapies is also developing creating a need for novel therapeutics.